Association between teat-end hyperkeratosis and mastitis in dairy cows: A systematic review

摘要

A systematic review was conducted to elucidate therole of teat-end hyperkeratosis (THK) as a risk factorfor clinical mastitis (CM) or subclinical mastitis (SCM).Scientific papers on the subject were identified bymeans of a database search. All types of peer-reviewedanalytical studies, observational or experimental andpublished in English, could be included in the review,regardless of publication year. Of 152 identified records,18 articles were selected, of which 8 were prospectivecohort studies, 9 were cross-sectional, and 1 was ahybrid case-control study. Internal validity of studieswas assessed using a score system ranging from 0 to 6,based on design, risk of bias, and statistical methods.The most frequent study limitation was improper use ofstatistical methods to avoid confounding of associationsbetween THK and CM or SCM. The 3 studies that usedCM as outcome (all with high validity scores) showedpositive associations with THK (especially severe),although the magnitude and statistical significance ofthe estimates differed among them. Most studies thatused SCM as the primary outcome (based on microbiologicalexamination of milk) reported that only severeTHK was associated with SCM. Two studies with highvalidity scores reported moderate to strong associationsbetween severe THK and incidence or prevalenceof Staphylococcus aureus intramammary infection. Twostudies with high validity scores reported that only severeTHK was associated with the risk of somatic cellcount (SCC) ≥200,000 cells/mL and increased meanSCC, respectively. Although 4 cross-sectional studiesreported positive associations between THK and SCC,these associations were possibly spurious because confoundingfactors, such as parity, were not considered inthe analyses. Results of the reviewed studies suggestthat severe THK is a risk factor for both CM and SCM,as defined by microbiological examination of milk, SCCthresholds, or mean SCC. The effect of severe THKon both contagious (especially Staphylococcus aureus)and environmental CM or SCM emphasizes the importanceof teat health for mastitis control. Four studiesdemonstrated that quarters with mild THK had lowerprevalence of intramammary infection or lower meanSCC than quarters with no THK, suggesting that developmentof mild THK, as a physiological response tomilking, can have a protective effect. Dairy consultantsshould focus on monitoring and minimizing occurrenceof severe THK to prevent CM and SCM.